Yes bad teachers exist. And I experience an injustice in high school.
To tell a short story there was a Biology teacher ,I was in her glass after lunch period,also I believe that was hers as well, She would come in give assignment to read some chapters then leave. We would not see her again until the next class day with the same missing act.
So report card period came and she gave most in her class F's I never got a f before, so my mother did not tolerate poor grades and I respected that.
So she requested a parent conference . It was in the principles office.
Never forget get it she claimed I never came to class, a lie ! She came but did not stay to teach her class,
So the principe ask me a question what biology my answer was not good enough !
So he explained it.
Next the principle went to all my classes even my hardest chemistry, geometry, and others my attendance was flawless .
So what he did was he decided to check on her classroom by intercome, he called her the first minutes of class ,she did not answer,gone!15 minutes later, no answer gone,45 minutes before the class bell ringed he came to the class gone no teacher.
The last I saw of that teacher was in the employment office years later.
Sad but these things happen.
And not to forget I was happy that those other teachers of mine kept good attendance records!